In a large pot, bring the chicken broth to a simmer over medium heat.
Add the sliced chicken, mushrooms, tofu, bamboo shoots, soy sauce, rice vinegar, grated ginger, minced garlic, and red pepper flakes to the pot. Stir well to combine.
Let the soup simmer for about 10-15 minutes until the chicken is cooked through and the vegetables are tender.
Slowly pour in the cornstarch mixture while stirring continuously to thicken the soup.
Drizzle the beaten egg into the soup while stirring gently to create egg ribbons.
Season with salt and pepper to taste.
Serve the hot and sour chicken soup hot, garnished with chopped green onions and cilantro.
Enjoy!